Using Windows Media Player for anything
is the first mistake.
Microsoft's obsession with DRM (digital rights management) makes anything done with that program problematic.
I have used TDK, Fuji, Maxell, and Verbatim CD-Rs in the stock head unit without difficulty. Memorex doesn't seem to work as well for some reason.
A few tips:
1. use CD-R only, CD-RW will not work
2. burn as an audio disc, MP3 and other data formats will not work
3. burn between 8x and 12x even if your recorder supports higher speeds.
4. test the burned disc in a regular CD player (not a computer recorder)
Try Nero, Easy Media Creator, or Instant CD/DVD for good commercial CD burning packages (Instant CD/DVD is only $10). Or get one of the freeware packages from a download site such as snapfiles.com. I've used DeepBurner before and CDBurnerXP gets good reviews.